CTLA4Ig introduced by adenovirus vector locally to prolong the survival of xenogeneic skin grafts on rat burn wounds

Immunological challenges associated with artificial skin grafts: available solutions and stem cells in future design of synthetic skin

The repair or replacement of damaged skins is still an important, challenging public health problem. Immune acceptance and long-term survival of skin grafts represent the major problem to overcome in grafting given that in most situations autografts cannot be used. The emergence of artificial skin substitutes provides alternative treatment with the capacity to reduce the dependency on the increasing demand of cadaver skin grafts. Over the years, considerable research efforts have focused on strategies for skin repair or permanent skin graft transplantations. Available skin substitutes include pre- or post-transplantation treatments of donor cells, stem cell-based therapies, and skin equivalents composed of bio-engineered acellular or cellular skin substitutes. However, skin substitutes are still prone to immunological rejection, and as such, there is currently no skin substitute available to overcome this phenomenon. This review focuses on the mechanisms of skin rejection and tolerance induction and outlines in detail current available strategies and alternatives that may allow achieving full-thickness skin replacement and repair.

The progress of Chinese burn medicine from the Third Military Medical University-in memory of its pioneer, Professor Li Ao

Professor Li Ao was one of the founders of Chinese burn medicine and one of the most renowned doctors and researchers of burns in China. He established one of the Chinese earliest special departments for burns at Third Military Medical University (TMMU) in 1958. To memorialize Professor Li Ao on his 100th birthday in 2017 and introduce our extensive experience, it is our honor to briefly review the development and achievement of the Chinese burn medicine from TMMU. The epidemiology and outcomes of admitted burn patients since 1958 were reviewed. Furthermore, main achievements of basic and clinical research for the past roughly 60 years were presented. These achievements mainly included the Chinese Rule of Nine, fluid resuscitation protocol, experience in inhalation injury, wound treatment strategies, prevention and treatment of burn infections, nutrition therapy, organ support therapies, and rehabilitation. The progress shaped and enriched modern Chinese burn medicine and promoted the development of world burn medicine.

CTLA4 enhances the osteogenic differentiation of allogeneic human mesenchymal stem cells in a model of immune activation

Allogeneic mesenchymal stem cells (allo-MSCs) have recently garnered increasing interest for their broad clinical therapy applications. Despite this, many studies have shown that allo-MSCs are associated with a high rate of graft rejection unless immunosuppressive therapy is administered to control allo-immune responses. Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) is a co-inhibitory molecule expressed on T cells that mediates the inhibition of T-cell function. Here, we investigated the osteogenic differentiation potency of allo-MSCs in an activated immune system that mimics the in vivo allo-MSC grafting microenvironment and explored the immunomodulatory role of the helper T cell receptor CTLA4 in this process. We found that MSC osteogenic differentiation was inhibited in the presence of the activated immune response and that overexpression of CTLA4 in allo-MSCs suppressed the immune response and promoted osteogenic differentiation. Our results support the application of CTLA4-overexpressing allo-MSCs in bone tissue engineering.

Self in vivo production of a synthetic biological drug CTLA4Ig using a minicircle vector

Cytotoxic T lymphocyte-associated antigen 4 immunoglobulin fusion protein (CTLA4Ig, abatacept) is a B7/CD28 costimulation inhibitor that can ward off the immune response by preventing the activation of naïve T cells. This therapeutic agent is administered to patients with autoimmune diseases such as rheumatoid arthritis. Its antiarthritic efficacy is satisfactory, but the limitations are the necessity for frequent injection and high cost. Minicircles can robustly express the target molecule and excrete it outside the cell as an indirect method to produce the protein of interest in vivo. We inserted the sequence of abatacept into the minicircle vector, and by successful in vivo injection the host was able to produce the synthetic protein drug. Intravenous infusion of the minicircle induced spontaneous production of CTLA4Ig in mice with collagen-induced arthritis. Self-produced CTLA4Ig significantly decreased the symptoms of arthritis. Injection of minicircle CTLA4Ig regulated Foxp3(+) T cells and Th17 cells. Parental and mock vectors did not ameliorate arthritis or modify the T cell population. We have developed a new concept of spontaneous protein drug delivery using a minicircle vector. Self in vivo production of a synthetic protein drug may be useful when biological drugs cannot be injected because of manufacturing or practical problems.

Transgenic expression of human cytoxic T-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) by porcine skin for xenogeneic skin grafting

Porcine skin is frequently used as a substitute of human skin to cover large wounds in clinic practice of wound care. In our previous work, we found that transgenic expression of human cytoxicT-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) in murine skin graft remarkably prolonged its survival in xenogeneic wounds without extensive immunosuppression in recipients, suggesting that transgenic hCTLA4Ig expression in skin graft may be an effective and safe method to prolong xenogeneic skin graft survival. In this work, using a transgene construct containing hCTLA4Ig coding sequence under the drive of human Keratine 14 (k14) promoter, hCTLA4Ig transgenic pigs were generated by somatic nuclear transfer. The derived transgenic pigs were healthy and exhibited no signs of susceptibility to infection. The hCTLA4Ig transgene was stably transmitted through germline over generations, and thereby a transgenic pig colony was established. In the derived transgenic pigs, hCTLA4Ig expression in skin was shown to be genetically stable over generations, and detected in heart, kidney and corneal as well as in skin. Transgenic hCTLA4Ig protein in pigs exhibited expected biological activity as it suppressed human lymphocyte proliferation in human mixed lymphocyte culture to extents comparable to those of commercially purchased purified hCTLA4Ig protein. In skin grafting from pigs to rats, transgenic porcine skin grafts exhibited remarkably prolonged survival compared to the wild-type skin grafts derived from the same pig strain (13.33 ± 3.64 vs. 6.25 ± 2.49 days, P < 0.01), further indicating that the transgenic hCTLA4Ig protein was biologically active and capable of extending porcine skin graft survival in xenogeneic wounds. The transgenic pigs generated in this work can be used as a reproducible resource to provide porcine skin grafts with extended survival for wound coverage, and also as donors to investigate the impacts of hCTLA4Ig on xenotransplantation of other organs (heart, kidney and corneal) due to the ectopic transgenic hCTLA4Ig expression.

Feasibility study of the sterilization of pigskin used as wound dressings by neutral electrolyzed water

BACKGROUND

Neutral electrolyzed water (NEW) is considered to be a high-level biodegradable disinfectant with sporicidal, bactericidal, and virucidal activity. It has also been reported to accelerate wound healing; thus, it is particularly attractive for the elimination or minimization of the microbial population of skin grafts to be used as wound dressings.

METHODS

Pigskins were sterilized with different concentrations of NEW and with different methods. The feasibility of pigskin sterilization by NEW was evaluated through microbiological analyses, viability assays, histologic assessments, contact cytotoxicity assays, and extract cytotoxicity assays.

RESULTS

NEW has strong bactericidal effects on pigskin microorganisms, does not change skin graft histologic properties, and has no cytotoxicity; however, skin viability was significantly reduced after NEW treatment.

CONCLUSION

Although NEW treatment is a very safe and effective method for nonviable pigskin dressing sterilization, to obtain a complete sterilization of pigskin grafts, available chlorine concentration of NEW as well as sterilization time and methods should be optimized.

Skin-specifically transgenic expression of biologically active human cytoxic T-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) in mice using lentiviral vector

Xenogeneic skin, especially porcine skin, has already been used to cover large wounds in clinic practice of wound care. Our previous data showed that transgenic expression of human cytoxic T-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) in murine skin graft remarkably prolonged its survival in xenogeneic burn wounds without extensive immunosuppression in recipients, suggesting that transgenic hCTLA4Ig expression in skin graft may be an effective and safe method to prolong its survival in xenogeneic wounds for coverage. Lentiviral transgenesis provides an extremely efficient and cost-effective method to produce transgenic animals. However, tissue-targeted transgenic expression of biologically functional protein by lentiviral transgenesis is rarely reported. In this work, a recombinant lentiviral vector (LV), named FKCW in this article, was constructed by inserting a skin-specific hCTLA4Ig expression cassette consisting of keratin 14 (K14) promoter, hCTLA4Ig coding sequence and an intronic fragment. Its efficacy for transgenesis and skin-specific expression of bio-active hCTLA4Ig protein was tested using mice as models. The LV FKCW was readily to be packaged and concentrated to high titres (1.287-6.254 × 10(9) TU/ml) by conventional lentivirus package system. Using eggs collected from only five mated females having been subjected to conventional super-ovulation treatment, 8 hCTLA4Ig transgenic founder mice were generated with the concentrated FKCW vector, and transgenic founder per injected and transferred egg was 6.3%, which was nearly 9-fold higher than that for DNA micro-injection with a similar transgene construct in our previous work. The lentiviral transgenic hCTLA4Ig exhibited strictly skin-specific expression at a level comparable to or even slightly higher than that of transgenic hCTLA4Ig delivered by micro-injection in a similar cassette. Lentiviral transgenic hCTLA4Ig protein remarkably suppressed human lymphocyte proliferation in vitro to a degree comparable to that of commercially purchased purified hCTLA4Ig protein with defined activity at similar concentrations. Besides, lentiviral hCTLA4Ig transgenic mouse skin grafted into rat burn wounds exhibited remarkably extended survival compared to wild-type skin of the same strain (13.8 ± 3.8 vs. 6.8 ± 3.0 days), indicating that lentiviral transgenic hCTLA4Ig did inhibit immune rejection against xenogeneic skin graft in vivo. These results laid down the foundation to further efficiently generate transgenic pigs skin-specifically expressing bio-active hCTLA4Ig by lentiviral transgenesis, and provided a demonstration that transgenic animals with tissue-targeted expression of biologically functional protein can be efficiently produced using LV.

In vitro Ad5F35-mediated CTLA4-Ig gene transfer prolongs pig skin xenotransplant survival

Wound closure and coverage are the biggest challenges faced by medical practitioners in treating severe burns. Fresh cadaver allografts are still considered to be the gold standard skin substitute. Unfortunately, their use is severely impeded by inadequate availability. In this report we endeavored to solve this problem by using gene-modified pig skin as a substitute for human skin. We report that adenovirus (Ad)-mediated transfer of human cytotoxic T-lymphocyte-associated antigen 4 immunoglobin (CTLA4-Ig) into pig skin in vitro is a useful approach to lower immunostimulatory ability and improve the take of pig skin for wound coverage. To optimize gene transfer efficiency, we also compared exogenous gene transfer efficiency in pig skin by Ad5F35 vector with that of the widely used Ad5. The uptake efficiency of Ad5F35 was about 1.3 times more than that of Ad5, and the survival time on rat burn wounds was prolonged by about 3 days. Our results demonstrate that CTLA4Ig gene-modified pig skin is a promising biologic dressing for wound coverage and Ad5F35 an effective viral carrier for delivery.

Embryonic porcine skin precursors can successfully develop into integrated skin without teratoma formation posttransplantation in nude mouse model

How to improve the wound healing quality of severe burn patients is still a challenge due to lack of skin appendages and rete ridges, no matter how much progress has been made in the fields of either stem cell or tissue engineering. We thus systematically studied the growth potential and differentiation capacity of porcine embryonic skin precursors. Implantation of embryonic skin precursors (PESPs) of different gestational ages in nude mice can generate the integrity skin, including epidermis, dermis and skin appendages, such as sweat gland, hair follicle, sebaceous gland, etc.. PESPs of embryonic day 42 possess the maximal growth potential, while, the safe window time of PESPs transplantation for prevention of teratoma risk is E56 or later. In conclusion, PESPs can form the 3 dimensional structures of skin with all necessary skin appendages. Our data strongly indicate that porcine embryonic skin precursors harvested from E56 of minipig may provide new hope for high-quality healing of extensive burns and traumas.

Transgenic expression of cytotoxic T-lymphocyte-associated antigen 4-immunoglobulin prolongs xenogeneic skin graft survival without extensive immunosuppression in rat burn wounds

BACKGROUND

We sought to establish a transgenic animal line skin-specifically overexpressing cytotoxic T-lymphocyte-associated antigen 4-immunoglobulin (CTLA4Ig) as a reproducible source of xenogeneic skin grafts with extended survival for wound coverage. We tested this strategy in mice based on a previously established transgenic mouse line that stably and skin-specifically expresses CTLA4Ig for lifetimes and generations.

METHODS

CTLA4Ig expression was examined by immunohistochemical assay, and its bio-activity was tested by mixed lymphocyte reaction. The survival of transgenic mouse skin grafted onto rat burn wounds was observed. The impact of transgenic skin grafting on recipient immunity was evaluated by inspecting the survival of the wild-type skin grafted along with transgenic skin onto a separate wound on the same rat. The circulatory CTLA4Ig protein in recipient was detected by sandwich enzyme-linked immunosorbent assay, and its impact on recipient lymphocyte response against donor antigen was tested by mixed lymphocyte reaction.

RESULTS

The transgenic CTLA4Ig protein suppressed lymphocyte proliferation in vitro, and the transgenic skin graft survival was remarkably prolonged compared with the wild-type skin derived from the same mouse strain. The survival of the wild-type skin grafted along with transgenic skin exhibited no significant difference from that grafted alone. Circulatory CTLA4Ig protein was detected in recipients, however, no significantly reduced recipient lymphocyte response against donor antigen was observed.

CONCLUSION

transgenic expression of CTLA4Ig may be a potential and safe method to prolong xenogenic skin graft survival in burn wounds, and transgenic animal lines can be established as a reproducible source of skin grafts with extended survival for wound coverage.

CTLA4-Ig-modified dendritic cells inhibit lymphocyte-mediated alloimmune responses and prolong the islet graft survival in mice

The induction of antigen specific tolerance is critical for prevention and treatment of allograft rejection. In this study, we transfected CTLA4-Ig gene into dendritic cells (DCs), and investigated their effect on inhibition of lymphocyte activity in vitro and induction of immune tolerance on pancreatic islet allograft in mice. An IDDM C57BL/6 murine model induced by streptozotocin is as model mouse. The model mice were transplanted of the islet cells isolated from the BALB/c mice to their kidney capsules, and injected of CTLA4-Ig modified DCs (mDCs). The results showed that mDCs could significantly inhibit T lymphocyte proliferation and induce its apoptosis; whereas, unmodified DCs (umDCs) promoted the murine lymphocyte proliferation. Compared with injection of umDCs and IgG1 modified DCs, the injection of mDCs prolonged IDDM mice's allograft survival, and normalized their plasma glucose (PG) levels within 3 days and maintained over 2 weeks. The level of IFN-gamma was lower and the level of IL-4 was higher in mDCs treated recipient mice than that in control mice, it indicated that mDCs led to Th1/Th2 deviation. After 7 days of islet transplantation, HE stain of the renal specimens showed that the islets and kidneys were intact in structure, and islet cells numbers are increased in mDCs treated mice. Our studies suggest that DCs expressing CTLA4-Ig fusion protein can induce the immune tolerance to islet graft and prolong the allograft survival through the inhibition of T cell proliferation in allogeneic mice.